Numerous technical and industrial processes require dispersion of a fluent material. One such dispersion process is atomization of a liquid into droplets. Atomization is employed in industrial processes such as combustion, chemical treatment of liquids, spray coating and spray painting. It is ordinarily desirable in dispersion processes such as atomization to produce a fine, uniform dispersion of the fluent material. Thus, in .atomization it is desirable to convert the liquid into fine droplets, most desirably droplets of substantially uniform size.
Considerable effort has been devoted heretofore to development of methods and apparatus for dispersing fluent materials. For example, mechanical atomizers which operate by forcing a liquid to be atomized under high pressure through a fine orifice. Such mechanical atomizers are used in oil burners and as fuel injectors in combustion engines. Other mechanical dispersion devices mix the fluent material to be atomized with a gas flowing at high velocity, so that the fluent material is dispersed by the kinetic effect of the high velocity gas.
A technique known as electrostatic atomization has also been employed. In electrostatic atomization, an electrical charge is applied to the fluent material, typically as the fluent material is discharged from an orifice. Because the various portions of the fluent material bear charges of the same polarity, various portions of the fluent material tend to repel one another. This tends to disperse the fluent material. In a rudimentary form of electrostatic atomization, the fluid is discharged from a nozzle towards a counterelectrode. The nozzle is maintained at a substantial electrical potential relative to the counterelectrode. This type of electrostatic atomization is used, for example, in electrostatic spray painting systems. Electrostatic atomization systems of this nature, however, can apply only a small net charge to the fluid to be atomized and hence the electrostatic atomization effect is minimal.
U.S. Pat. No. 4,255,777 discloses a different electrostatic atomization system. As taught in the '777 patent, the fluid may be passed between a pair of opposed electrodes before discharge through the orifice. These opposed electrodes are maintained under differing electrical potentials, so that charges leave one of the electrodes and travel towards the opposite electrode through the fluid. However, the moving fluid tends to carry the charges downstream, towards the discharge orifice. Generally, the velocity of the fluid is great enough that most all of the charges pass downstream through the orifice and do not reach the opposite electrode. Thus, a net charge is injected into the fluid by the action of the opposed electrodes. Systems according to the '777 patent can apply substantial net charge to the fluid and hence can provide superior atomization.
Systems according to the '777 patent, however, can only be applied where the fluid has relatively low electrical conductivity, typically below about 1 microSiemens per meter. Where the electrical conductivity of the fluid is substantially greater than 1 microSiemens per meter, it is difficult to maintain a substantial potential difference between the electrodes. Although numerous organic liquids can be successfully atomized by the methods and apparatus of the '777 patent, many other industrially significant materials are too conductive and hence cannot be atomized or dispersed by the methods and apparatus of the '777 patent. For example, typical aqueous solutions of inorganic materials are highly conductive and hence not readily susceptible to electrostatic atomization according to the method of the '777 patent. These conductive solutions include industrially important material such as water based paints and coatings, comestible materials such as beverage extracts and agricultural materials such as aqueous fertilizer solutions, herbicide solutions and the like.
U.S. Pat. No. 4,618,432 briefly mentions the possibility of using an electron beam to apply a net charge to a liquid (Column 6, line 19), but offers no teaching of how to do so. U.S. Pat. Nos. 4,218,410 and 4,295,808 and Mahoney et al., Fine Powder Production Using Electrohydrodynamic Atomization, conference paper, IEEE-IAS 1984 annual meeting, suggest formation of a metal powder by processes wherein an electron beam impinges on a mass of metal under high vacuum conditions. U.S. Pat. Nos. 2,737,593 and 3,122,633 refer to treatment of liquids by electron beams for purposes other than atomization. U.S. Pat. Nos. 3,636,673; 4,112,307; 4,663,532 and 4,631,444 are directed to various structures employing an electron-permeable membrane, also referred to as an "electron window". A paper by A. Mizuno, Use of an Electron Beam for Particle Charging, IEEE Transactions on Industry Applications, Vol. 26, No. 1 (January/February 1990) discusses the use of electron-beam ionization in a precharger for an electrostatic precipitator and the extraction of negative ions and free electrons from the ionization zone by an applied electric field.
Despite these efforts in the prior art, there has been a substantial, unmet need heretofore for improved methods and apparatus of dispersion. The present invention addresses these needs.